The present invention relates to an apparatus for detecting an abnormality of a relay, and more particularly, to an apparatus for detecting an abnormality of a relay used in a controller of a drive force transmission.
A controller is used for a drive force transmission of a four wheel drive vehicle to activate and deactivate a relay that is incorporated or externally attached. The drive force transmission includes a clutch mechanism and an electromagnetic coil for connecting and disconnecting the clutch.
The controller activates the relay and controls the activation and de-activation of a switching transistor to control the amount of current supplied to the electromagnetic coil from a power supply via the relay. When the electromagnetic coil is excited, the clutch mechanism is connected and torque distribution is performed to achieve four wheel drive.
Such a controller determines whether the relay has an abnormality when an ignition switch (power supply switch) goes on. The detection of an abnormality of the ignition switch includes detecting whether a relay contact has fused (fusion detection) and detecting whether the relay has remained opened (open abnormality detection).
During open abnormality detection, the controller activates and deactivates the relay once to check the voltage of circuits connected to the relay and detect whether there is an open abnormality. When an open abnormality is detected, a fail safe process is immediately performed.
However, if there is a contact failure when the relay is activated and deactivated once and the contact returns to normal afterward, the controller erroneously detects a relay abnormality.